Hydrotreating process utilizing alkyl disulfide for in situ catalyst activation



United States Patent C U.S. Cl. 208216 4 Claims ABSTRACT OF THEDISCLOSURE A process for activating and initiating reaction on anickel-molybdenum hydrotreating catalyst, which provides superioraromatic saturation and nitrogen and sulfur removal, is provided by thesteps of treating the catalyst with hydrogen at low pressure whileheating to about 350 F., pressurizing to about 300-2500 p.s.i.g. andsulfiding with a hydrocarbon stock containing about 1 to 5% disulfidesulfur with a hydrogen flow rate of about 1000-2500 s.c.f./b., at atemperature of about 675- 700 F., taking care that the temperature doesnot exceed 750 F. at any point in the reactor. Processing is theninitiated with a substantial excess of hydrogen for the first 24 to 72hours.

This invention relates to a process for the catalytic hydrotreating ofhydrocarbon oils of at least 90% by volume boiling above about 300 C.More particularly, it relates to a process for the catalytichydrotreating of hydrocarbon oils containing aromatic unsaturatedconstituents and sulfurand nitrogen-bearing compounds. Mostparticularly, it relates to a process whereby the activity of thehydrotreating catalyst is enhanced both for the hydrogenation ofunsaturated constituents and the removal of sulfur and nitrogen atoms.

Various high boiling hydrocarbons have been hydrotreated under varyingconditions of temperature, pressure, and contact time, depending on theparticular catalyst and the particular oil feed, to effect a substantialconversion of the oil to lower boiling products. When carried out withthis result, such operation is referred to as destructive hydrogenationor hydrocracking. This invention does not relate to such hydrotreatingprocesses. While hydrocracking is desired in some processes, there arecases where it is undesirable and is avoided, e.g. in the hydrotreatingof lubricating oil and the like.

Hydrotreating under conditions where not more than of the feed oil isconverted to lower boiling products is often referred to asnon-destructive hydrogenation or hydrotreating. There is usually atleast a small amount of lower boiling material unavoidably produced dueto the extraction of sulfur and nitrogen atoms from the sulfurandnitrogen-bearing compounds which are normally present in the feed, butlower boiling material is not desired. It is to such non-destructivehydrotreating processes that the present invention relates.

The non-destructive hydrogenation of hydrocarbon oils may be efiected inseveral ways. In one type of operation, for example, hydrocarbon oilscontaining aromatic unsaturated constituents and sulfurandnitrogen-bearing compounds are hydrotreated with a catalyst containing ametal or metal oxide which is capable of extracting and reacting withsulfur in the oil. The catalyst also serves to promote hydrogenation ofunsaturated constituents and to remove nitrogen from the oils. In thistype of process, which may be called regenerative, the process isstopped as soon as the metal has been substantially converted to thesulfide (as manifested in the appearance of hydrogen sulfide in thereactor efiluent), the catalyst is regenerated or roasted to convert themetal sulfide back to the active oxide or metallic form, and a newprocess period is then started. The process periods between successiveregenerations of the catalyst are normally quite short. Since it isnecessary to free the catalyst of oil preceding each regeneration, it isonly practical to operate this type of process when treating lowboiling, easily volatilized feeds or to ensure that the feed oil, ifheavy, is completely volatilized by the use of a large amount of gas.This invention does not relate to such regenerative processes.

The more preferred type of hydrotreating process is one in which the oiland hydrogen gas are passed substantially continuously in contact with afixed bed of a suitable hydrotreating catalyst. The processes to whichthe present invention relates are of this type, usually referred to asnon-regenerative processing. And regeneration is only required after arelatively long period of continuous use, usually measured in aplurality of weeks or months.

The catalysts found suitable for the non-regenerative hydrotreatingprocesses comprise one or more metals selected from Group VIII of theperiodic chart of the elements and one or more metals of Group VI, andordinarily are supported on an alumina or silica-alumina base. Themetals may have been prepared initially in their metallic form or in theform of compounds with oxygen or sulfur. During use, however, they arepresent in an activated form as sulfides. Thus, the catalyst may beprepared from the metal sulfides, or it may be sulfided prior to use, orit may become sulfided during the initial stages of the process itself.

This process relates to hydrotreating catalysts comprising nickel andmolybdenum as the active metal component. The particular catalysts arewell known and are available commercially, as, for instance, AmericanCyanamids HDS-3 or HDS-3A, in the form of nickel and molybdenum oxideson an alumina or silica-alumina base. Such catalysts, when activated byconversion of the metal oxides to sulfides, are highly active both inthe hydrogenation of aromatic constituents and in the removal of sulfurand nitrogen from the feed.

The nickel-molybdenum hydrotreating catalysts are significantly moresensitive than other hydrotreating catalysts, such as for instancecobalt-molybdenum or cobalttungsten, to the activation processesordinarily employed to convert the metals to their sulfides.Difliculties are encountered in achieving full activity of thenickel-molybdenum catalysts, in that the nickel oxide component isreadily reduced to the metallic form and, as such, is rendered almostincapable of conversion to the sulfide necessary to obtain the fullestactivity. The activation processes known for the activation ofnickel-molybdenum hydrotreating catalysts include sulfiding with astream of hydrogen sulfide gas; a mixture of hydrogen sulfide andhydrogen; a mixture of hydrogen and a mercaptan, a sulfide, or adisulfide; a high sulfur content hydrocarbon stream; and the sulfurcontaining hydrocarbon feed to be processed. None of these processes hasproved completely satisfactory in achieving the full activity of thecatalyst and are decidedly inferior to the activation process of thisinvention, particularly in accomplishing saturation of aromatic carbonrings to the fullest extent.

In the process of the present invention, the catalyst is activated bycontacting it in the hereinafter prescribed manner first with hydrogenalone and then with a mixture of hydrogen and a distillate of mediumviscosity containing from about 1 to about 5 percent of disulfidesulfur. The particular sulfiding medium is not, however, alonesufl'icient in order to most effectively activate the catalyst.

3 It is additionally necessary to maintain process conditions withincertain prescribed limits.

The process of the present invention comprises first purging thecaltalyst bed of air. Ordinarily, the reactor containing the catalystbed is evacuated and then the system is purged with nitrogen until theoxygen content is reduced to less than about 2%. Once the reactor systemis purged, the nitrogen is displaced with hydrogen or a hydrogen-richgas. The reactor is then heated to a temperature of about 350 F.,preferably in as short a time as possible, at a hydrogen flow raterelative to a feed of processing stock or sulfiding medium at 0.4 WHSVof from about 1000 to 2500 s.c.f./b., and at a pressure not greater thanabout 50 p.s.i.g. When the temperature has reached about 400 F., thesystem is pressurized to about 300 to 2500 p.s.i.g. with the hydrogengas. It is necessary not to create a pressure of greater than about 50p.s.i.g. before attaining the 400 F. temperature to avoid entrappingwater absorbed or adsorbed on the catalyst which will cause sinteringand preclude satisfactory activation of the catalyst. When the reactoris fully pressurized at about 400 F., the sulfiding stock is cut in. Thesulfiding stock preferably has a viscosity of about 30 to 100 S.S.U. at100 F. and is a distillate containing from about 1 to 5 weight percentsulfur as disulfide compounds, e.g. R-S-S-R where R may be a methyl,ethyl, butyl or higher radical, or a mixture of such compounds. The feedshould be passed through the reactor at about 0.25 to 1.0 WHSV and thehydrogen gas should be maintained at about the same rate of flow asbefore, or at 1.5-3 times the rate of consumption. The temperature isgradually increased at about 100 F. per hour from about 400 F. to about675700 F., taking care that the temperature does not exceed 725 F. atany point in the reactor. Once the desired temperature is attained, theprocessing is continued for at least 6 hours, and preferably for 24hours or even longer. The sulfiding medium is then cut out and the stockto be processed is fed at a WHSV of 0.2 to 5.0. The hydrogen rate is setat from about 300 to 5000 s.c.f./b. at the operating pressure of theprocess, or at least about twice the rate of consumption, and thetemperature is maintained at the 675 F. to 700 F. range. Processing iscontinued under these conditions for at least about 48 hours, andpreferably about 72 hours before conditions are altered to normaloperating levels for the hydrotreating process.

When conducted as described, the process provides a nickel-molybdenumhydrotreating catalyst of exceptional activity, both for providingaromatic saturation and for the removal of sulfur and nitrogen.

EXAMPLES I-III A hydrotreating HDS-3A catalyst comprising 2.3 weightpercent nickel oxide and 15.6 weight percent molybdenum oxide on analumina support was activated by three different sulfiding processes.After activation, the catalyst from each process was utilized forhydrotreating a medium viscosity, non-waxy lube distillate feed,processed at 700 F. 0.25 WHSV, and with 1500 s.c.f./b. of hydrogen at1500 p.s.i.g. The pertinent characteristics of the feedstock appear inTable I In the first process, the catalyst was reduced for 2 hours at500 F. with hydrogen gas at atmospheric pressure with a flow of 20s.c.f. of hydrogen per kilogram of catalyst. After the H reduction, thecatalyst was treated with hydrocarbon feedstock at 700 F., 1500p.s.i.g., and at 1.0 WHSV in the presence of 1500 s.c.f./b. for 193hours of conditioning under process conditions, the reaction product wastested for catalyst activity reported below in Table I as process 1.

A second catalyst charge was purged with nitrogen and then pressurizedto 80 p.s.i.g. with hydrogen. Under 10 s.c.f. of hydrogen per hour perkilogram of catalyst, the temperature was raised to 400 F. and 0.2s.c.f. of

H S per hour per kilogram of catalyst was injected into the hydrogenstream for 24 hours. At the end of the sulfiding processing, the chargewas conditioned for 24 hours with feedstock at 700 F., 1500 p.s.i.g., at1.0 WHSV with 1500 s.c.f./b. of hydrogen and the product was tested withthe results reported on Table I. under process 2.v

In the third process, after a nitrogen purge at low temperature, thecatalyst charge was treated with hydrogen to bring the temperature to400 F. with a flow rate of 10 s.c.f. hydrogen per kilogram of catalystat atmospheric pressure. At the 400 F. temperature, the system waspressurized to 1500 p.s.i.g. and a light gas oil stock containing 5%disulfide sulfur at 0.4 WHSV and the hydrogen rate was adjusted to 1500s.c.f./ b. The temperature was increased at F. per hour to a maximum of700 F. and the processing was continued for 24 hours, and the sulfidingstock was then replaced with the hydrocarbon feed, the space velocitychanged to- 0.25, and conditioning was continued for 48 hours beforeprocessingconditions were further altered. The hydrotreated stock wasthen tested and appears in Table I as process 3.

EXAMPLES IV-VI Three catalyst samples of a commercially availablehydrotreating catalyst of nickel and molybdenum oxides on an aluminabase were activated in the following manner. After purging withnitrogen, the catalyst beds were heated to 400 F. with a flow of 20s.c.f. of hydrogen per kilogram of catalyst atmospheric pressure. Thesystems were then pressurized to 1500 p.s.i.g. and a light gas oilsulfiding stock containing 1.85% disulfide sulfur was passed through thereactor at 1.0 WHSV with 1500 s.c.f./ b. hydrogen. The temperature wasincreased at 100 F. per hour to 700 F. Two of the catalyst samples werepermitted to exceed 750 F. for a short time during the sulfidingprocess, while the third was not allowed to exceed 725 F. at any time.The sulfiding was continued for 48 hours for the first overheatedsample, reported as 4 in Table II, and the sample maintained at below725 F reported as 6 in Table II. The remaining overheated sample, number5 in Table II, was processed for 144 hours. At the conclusion of thesulfiding step, a medium viscosity, non-waxy lube distillate wasintroduced as feed on each catalyst and was processed at 700 F., 1500p.s.i.g. and 0.25 WHSV with 1500 s.c.f./b. hydrogen. After 12 hours onstream, inspection tests on the nitrogen stripped product (to remove H8) showed the results reported in Table II.

Comparison of the results of runs 4 and 5 with those of run 6 indicatethe necessity of maintaining the catalyst at temperatures below 750 F.during the sulfiding step.

Even the increased processing time in run 5 did not serve to improve theactivity of the overheated catalyst sample.

EXAMPLES VII-IX In the following Table III, a light, non-waxy lubedistillate of about 60 SUS at 100 F. containing 5% disulfide sulfur wasutilized as indicated as sulfiding stock. The feedstock processed wasthe same as in Table II, as were conditions of feedstock processing.

TABLE III Activation process 7 8 9 sulfidingprocess conditions:

WHS ,lb. /hr./lb. c 1.0 0. 25 0.40

Pressure, p.s.i.g 1, 500 1,500 1, 500

H2 rate, s.c.f.[b 2, 500 2, 500 1, 560

Temperature, F 650 650 650 Sulfiding time, hrs 48 48 48 Activity test:

Gravity, API 26. 27. 9 29. 0

Refractive index, no 1. 4860 1. 4827 1.4790

Specific dispersion 102. 6 105. 1 101. 0

Sulfur content, p.p.m 10 10 Nitrogen content, p.p.m 1. 8 2. 7 1. 8

Hydrogen content, wt. percent 13. 36 13. 31 13. 52

A comparison of the results indicates less than optimum activity in run8. The lower space velocity in this run results possibly in exposure ofthe catalyst in the lower part of the bed to hot hydrogen which reducesnickel and/or molybdenum to the metallic form, rather than formation ofthe sulfide. In run 9, where a near optlmum is achieved, the hydrogenrate is balanced with the space velocity and sulfur content.

EXAMPLE X Example X illustrates a further requirement in the activationof the catalyst for hydrotreating, i.e., the manutenance of the hydrogengas rate considerably in excess of the rate of consumption for a periodof 24 to 72 hours after the initiating of feedstock processing at theconclusion of the sulfiding process. Hydrogen starvation has proved topermanently damage catalyst activity and aromatic saturation andnitrogen removal will be less than optimum. In Table IV, two processingruns are shown, utilizing the feed of Table II on two catalysts sulfidedunder identical conditions.

A comparison of the two runs, wherein the hydrogen gas rate is the onlysignificant process variable, indicates about the same flushhydrocracking activity, as measured by API gravity, and sulfur removal.Run B, however, shows significantly better aromatic saturation andnitrogen removal.

It is claimed:

1. A process for hydrotreating a hydrocarbon stock in a system includinga catalyst comprising nickel and molydenum oxides on a base selectedfrom the group consisting of alumina and silica-alumina disposed in ahydrotreating zone comprising the steps of (a) contacting the catalystin said hydrotreating zone with a flow of hydrogen gas while heating thecatalyst to a temperature of about 350 F. with the pressure being notgreater than about 50 p.s.i.g,

(b) increasing the pressure to about 300 to 2500 p.s.i.g,

(c) contacting said catalyst with hydrogen and a hydrocarbon gas oil orlube distillate sulfiding stock containing from about 1 to 5 weightpercent sulfur as alkyl disulfide, the alkyl groups of which have 1 to 4carbon atoms, at a WHSV of from about 0.25 to 1.0, a pressure of fromabout 300 to 2500 p.s.i.g, and a temperature of from about 675 to 700 F.with hydrogen at a flow rate of from about 1000 to 2500 s.c.f./b., saidtemperature never exceeding 750 F. in any part of the system, with thesulfiding step being maintained for a period of from about 24 to 72hours,

((1) stopping the sulfiding stock, and

(e) passing said hydrocarbon feedstock in contact with said catalyst andhydrogen at a hydrogen flow rate of at least about 300 to 5000 s.c.f./b.for at least about 48 hours.

2. The process of claim 1 wherein the temperature of the sulfiding stepnever exceeds 725 F.

3. The process of claim 1 wherein the hydrocarbon feedstock which issubjected to hydrotreating is a hydrocarbon oil having at least byvolume boiling above about 300 C.

4. The process of claim 1 wherein the hydrocarbon sulfiding stock has aviscosity of about 30 to S.S.U. at 100 F.

References Cited UNITED STATES PATENTS 3,016,347 1/ 1962 OHara.

3,109,804 11/1963 Martin 208216 3,114,701 12/1963 Jacobson et al 2524393,239,450 3/ 1966 Lindquist et a1. 252--439 3,256,205 6/1966 Constabariset a1. 252-415 3,291,751 12/1966 Buss 252439 3,364,150 1/1968 Hughes 252439 DELBERT E. GANTZ, Primary Examiner G. J. CRASANAKIS, AssistantExaminer US. Cl. X.R. 208--254; 252-439

